Method for manufacturing interdental cleaning tool

ABSTRACT

To provide method for manufacturing interdental cleaner for suppressing elastomer from insufficiently filling into space around shaft portion in filling the elastomer into mold. Method for manufacturing interdental cleaner includes first step of molding base portion having handle portion and shaft portion (40) by filling composite material into first mold, and second step of forming cleaning portion, slip resistance portion and coupling portion by filling elastomer into second mold (200) from distal end portion side of shaft portion (40) with base portion situated in second mold (200), second mold (200) having second space for forming cleaning portion, slip resistance portion and coupling portion. What is used as second mold (200) in second step has ratio no less than 40% of a flow path area in second space for elastomer around distal end portion of handle portion to flow path area in second space for elastomer around proximal end portion of shaft portion (40).

BACKGROUND OF THE INVENTION (1) Field of the Invention

The present invention relates to a method for manufacturing aninterdental cleaner.

(2) Description of Related Art

Conventionally, there is a known interdental cleaner especially suitablefor cleaning an interdental space between back teeth. Patent Literature1 discloses, for example, an interdental cleaner including a basematerial portion made of synthetic resin and a soft portion made ofelastomer. The base material portion has a handle base and a thinshaft-shaped core portion. The handle base has a curved shape. Anannular recessed portion is formed in the handle base. The soft portionhas a cleaning soft portion formed around the core portion, a slipresistance portion formed around the annular recessed portion, and acoupling portion coupling the cleaning soft portion and the slipresistance portion. A sectional area of the coupling portion is smallerthan respective sectional areas of the cleaning soft portion and theslip resistance portion.

The interdental cleaners are manufactured by performing a first step ofmolding the base material portions (primary molded products) and asecond step of molding the interdental cleaners (secondary moldedproducts) by forming the soft portions on the respective base materialportions. In detail, in the first step, the base material portions(primary molded products) are molded by filling the synthetic resin intoa first mold having spaces in correspondence to the base materialportions. In the subsequent second step, the elastomer is filled into asecond mold having spaces for forming the soft portions around therespective base material portions under a condition in which the basematerial portions is situated in the second mold. In detail, theelastomer is filled into the second mold from gates formed at positionsin correspondence to portions of the respective base material portionsbetween the respective core portions and the respective annular recessedportions. In the second step, the cleaning soft portions configured toclean interdental spaces are formed by filling the elastomer around therespective core portions, the slip resistance portions are formed byfilling the elastomer into the respective annular recessed portions inthe respective handle bases, and the coupling portions are formed byfilling the elastomer to surfaces of portions of the base materialportions between the core portions and the annular recessed portions.Through the aforementioned steps, the interdental cleaners (secondarymolded products) respectively including the base material portions andthe soft portions are molded.

CITATION LIST Patent Literature

Patent Literature 1: JP 2016-104382 A

BRIEF SUMMARY OF THE INVENTION Problem to be Solved by the Invention

With regard to the interdental cleaner described in Patent Literature 1,insufficient filling of the elastomer into a space especially around avicinity of a distal end of the core portion (incomplete molding of thecleaning soft portion) may occur in the second step.

An object of the present invention is to provide a method formanufacturing an interdental cleaner configured to suppress occurrenceof insufficient filling of elastomer into a space around a shaft portionin a step of filling the elastomer into a mold.

Solution to Problem

To solve the aforementioned problem, it is considered to fill theelastomer into the second mold from a side of a distal end portion ofthe shaft portion in the second step. In this way, it is possible tosuppress the occurrence of the insufficient filling of the elastomerinto the space around the shaft portion. However, a sectional area ofthe coupling portion (an elastomer flow path area of a region of thesecond space in correspondence to the coupling portion) is smaller thanrespective sectional areas of the cleaning portion and the slipresistance portion, so that a pressure loss becomes large when theelastomer flows through the space in correspondence to the couplingportion. To cope with this, a very large injection pressure is required,but the elastomer may leak from a space for forming the coupling portionto the outside of the space.

According to the present invention, there is provided a method formanufacturing an interdental cleaner including: a first step of moldinga base portion by filling composite material including synthetic resininto a first mold having a first space in correspondence to the baseportion which includes a handle portion having a shape that is at leastpartially curved and a shaft portion connected to a distal end portionof the handle portion, the shaft portion having a sectional area smallerthan a sectional area of the handle portion and a shape which allows theshaft portion to be inserted into an interdental space; and a secondstep of forming a cleaning portion configured to clean the inter dentalspace, a slip resistance portion and a coupling portion configured tocouple the cleaning portion and the slip resistance portion by fillingelastomer into a second mold from a side of a distal end portion of theshaft portion under a condition in which the base portion is situated inthe second mold, the second mold having a second space configured toform the cleaning portion around the shaft portion, the slip resistanceportion on a surface of the handle portion, and the coupling portion ona surface of the handle portion. What is used as the second mold in thesecond step has a ratio of a flow path area for the elastomer in asection of the second space around the distal end portion of the handleportion to a flow path area for the elastomer in a section of the secondspace around a proximal end portion of the shaft portion, the ratiobeing no less than 40%.

According to this manufacturing method, what is used in the second stepas the second mold has the ratio of the flow path area in the secondspace for the elastomer around the distal end portion of the handleportion to the flow path area for the elastomer in the second spacearound the proximal end portion of the shaft portion, the ratio being noless than 40%. In this way, it is possible to suppress a very largepressure loss in the second step when the elastomer flowing along theshaft portion from the side of the distal end portion of the shaftportion flows through the space in correspondence to the couplingportion. Therefore, the elastomer flows smoothly from the space aroundthe shaft portion toward the space in correspondence to the slipresistance portion through the space in correspondence to the couplingportion. In this way, it is possible to suppress leakage of theelastomer from the second spaces in the second step.

In detail, what is used as the second mold in the second step has theratio which is no more than 90%.

In this way, a pressure loss is secured to some extent when theelastomer flows through the space in correspondence to the couplingportion, so that it is possible to suppress occurrence of incompletemolding of the cleaning portion.

In the method for manufacturing the interdental cleaner, in the firststep, what is molded preferably has the handle portion including a baseand a recessed portion having a shape recessed from a surface of thebase, the handle portion including a back-side edge portion, which isformed on one side in a direction orthogonal to an axial direction ofthe shaft portion to have a curved shape so that the recessed portion isformed at a position including at least a part of the back-side edgeportion, and a belly-side edge portion, which is formed on another sideto have a curved shape so that the base is formed at a positionincluding at least a part of the belly-side edge portion, an anglebetween a tangent to a distal end portion of the back-side edge portionand the axial direction of the shaft portion being smaller than an anglebetween a tangent to a distal end portion of the belly-side edge portionand the axial direction of the shaft portion. In the second step, theelastomer is filled into the second mold so that the elastomer flowsalong the shaft portion and the recessed portion.

In this way, the elastomer smoothly flows from a periphery of the shaftportion toward the recessed portion. Since the handle portion isslightly displaced toward a belly side of the handle portion in thesecond mold due to an injection pressure of the elastomer, a flow pathfor forming the coupling portion is secured.

In this case, in the first step, what is molded as the base portionpreferably includes the base having a shape extending continuously alongthe belly-side edge portion.

In this way, since the base made of the composite material extendscontinuously along the belly-side edge portion, the handle portion hashigher strength as compared to the case in which a part of the slipresistance portion made of the elastomer is provided along thebelly-side edge portion, for example.

In this case, in the first step, it is preferable that what is molded asthe handle portion further includes a bulge portion bulging from aportion of a surface of the recessed portion at a distance from aboundary between the base and the recessed portion.

In this way, the elastomer flowing along the recessed portion in thesecond step collides with a side surface of the bulge portion beforecolliding with the boundary between the recessed portion and the base (aside surface rising from a proximal end portion of the recessedportion), so that a flow velocity of the elastomer reduces. In this way,the elastomer is prevented from strongly colliding with the boundarybetween the recessed portion and the base. As a result, it is possibleto suppress leakage of the elastomer from the second space in the secondmold to an outside of the second space in the second step.

Moreover, in the first step, what is molded as the recessed portionpreferably includes a flow path widening region in which a flow patharea for the elastomer at a portion distant by 1 mm from a specificportion of the recessed portion to an opposite side from the shaftportion is larger by no less than 7% in comparison with a flow path areafor the elastomer at the specific portion, and the bulge portion whichis at least partially situated in the flow path widening region.

In this way, it is possible to manufacture the interdental cleaner withan effective slip resistance function of the slip resistance portionwith suppressing occurrence of jetting (external visual defects ofelastomer flow marks) in the flow path widening region when theelastomer flows along the recessed portion in the second step. Indetail, if the flow path area in the recessed portion for the elastomerincreases abruptly when the elastomer flows along the recessed portion,the jetting may happen to a vicinity of the position of the abruptincrease in the flow path area. With regard to this manufacturingmethod, since at least a part of the bulge portion is situated in theflow path widening region, the occurrence of the jetting resultant fromthe increase in the flow path area is suppressed.

In the method for manufacturing the interdental cleaner, preferably, inthe first step, the composite material including the synthetic resin andglass fiber is filled into the first mold.

In this way, since the base portion reinforced with the glass fiber ismolded in the first step, it is possible to suppress damage to the bulgeportion even if there is a contact between the bulge portion and thesecond mold when the base portion is situated in the second mold.Vibration of the base portion when the base portion is situated in thesecond mold may be suppressed as well.

In this case, preferably, in the first step, the composite materialfurther including titanium dioxide is filled into the first mold.

Although the reinforcing effect of the glass fiber on the base portionis slightly reduced by inclusion of titanium dioxide, the bulge portionprovided to the base portion suppresses the reduction in strength of thehandle portion resultant from the inclusion of titanium dioxide, and theresultant vibration of the base portion when the base portion issituated in the second mold. It is also possible to mold the white baseportion at low cost.

Effect of Invention

As described above, according to the present invention, it is possibleto provide a method for manufacturing an interdental cleaner configuredto suppress occurrence of the insufficient filling of the elastomer intothe space around the shaft portion in the step of filling the elastomerinto the mold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of an interdental cleaner group according to anembodiment of the present invention.

FIG. 2 is a front view of the interdental cleaner.

FIG. 3 is a left side view of the interdental cleaner shown in FIG. 2.

FIG. 4 is a front view of a base portion of the interdental cleanershown in FIG. 2.

FIG. 5 is a sectional view taken along line V-V in FIG. 2.

FIG. 6 is a sectional view taken along line VI-VI in FIG. 2.

FIG. 7 is a sectional view taken along line VII-VII in FIG. 2.

FIG. 8 is a sectional view taken along line VIII-VIII in FIG. 2.

FIG. 9 is a view showing a first mold.

FIG. 10 is a view showing a second mold and the base portion.

DETAILED DESCRIPTION OF THE INVENTION

An of interdental cleaner group 1 according to an embodiment of thepresent invention is described with reference to FIGS. 1 to 10. As shownin FIG. 1, the interdental cleaner group 1 includes interdental cleaners2 connected to each other. The interdental cleaners 2 adjacent to eachother are connected by connecting portions 32. Each of the interdentalcleaners 2 has a base portion 10 (c.f. FIG. 4) made of compositematerial including synthetic resin and a soft portion 50 (c.f. FIG. 3)made of elastomer having hardness lower than that of the compositematerial. The composite material is material including the syntheticresin, glass fiber and titanium dioxide. A glass fiber content in thecomposite material is preferably 10 to 49% by weight, and morepreferably 15 to 45% by weight. A titanium dioxide content in thecomposite material is preferably 0.5 to 10% by weight, and morepreferably 1 to 5% by weight. With regard to the present embodiment, theglass fiber content is 30% by weight, and the titanium dioxide contentis 3% by weight. Polypropylene, ABS, polybutylene terephthalate,polycarbonate, polyethylene terephthalate, polystyrene, polyacetal orthe like is preferably used as the synthetic resin. Styrene elastomer,silicon, olefin elastomer, polyester elastomer or the like is preferablyused as the elastomer. With regard to the present embodiment,polypropylene is used as the synthetic resin, and styrene elastomer isused as the elastomer.

The respective interdental cleaners 2 are manufactured by performing thefollowing first and second steps. In the first step, the base portions(primary molded products) 10 are molded by filling the compositematerial into a first mold 100 (c.f. FIG. 9) having a first space incorrespondence to the base portions 10. In the second step, theinterdental cleaners (secondary molded products) 2 respectively havingthe soft portions 50 are manufactured by filling the elastomer into asecond mold 200 (c.f. FIG. 10) having second spaces configured to formthe soft portions 50 under a condition in which the base portions 10 aresituated in the second mold 200. Details of the manufacturing method aredescribed later.

As shown in FIG. 4, the base portion 10 has a handle portion 20 to beheld by fingers and a shaft portion 40 connected to a distal end portion(upper end portion in FIG. 4) of the handle portion 20.

The handle portion 20 has a shape curved at least partially. With regardto the present embodiment, the handle portion 20 is formed in a flatshape. The handle portion 20 has a handle main body 22 and a heldportion 30.

With regard to the present embodiment, the handle main body 22 has ashape which is curved entirely. The handle main body 22 has a belly-sideedge portion 22 a and a back-side edge portion 22 b. The belly-side edgeportion 22 a is a portion which is formed on one side (a right side inFIG. 4) of the handle main body 22 in a direction orthogonal to an axialdirection of the shaft portion 40 to have a curved shape. The back-sideedge portion 22 b is a portion which is formed on the other side (a leftside in FIG. 4) of the handle main body 22 in the direction orthogonalto the axial direction of the shaft portion 40 to have a curved shape. Asize of the handle main body 22 in a width direction (a directionconnecting the belly-side edge portion 22 a and the back-side edgeportion 22 b) is larger than a thickness of the handle main body 22. Thehandle main body 22 has a base 24, a recessed portion 26 and bulgeportions 28.

The base 24 includes the belly-side edge portion 22 a and has a curvedshape.

As shown in FIGS. 7 and 8, the recessed portion 26 has a shape recessedfrom surfaces of the base 24. The recessed portion 26 includes theback-side edge portion 22 b and has the curved shape. The recessedportion 26 is formed on both surfaces of the handle main body 22. Asshown in FIG. 4, the recessed portion 26 has a flow path widening region26A. The flow path widening region 26A is a region in which a flow patharea for the elastomer at a portion distant by 1 mm from a specificportion of the recessed portion 26 to an opposite side from the shaftportion 40 (downward in FIG. 4) is larger by no less than 7% incomparison to a flow path area for the elastomer at the specificportion. In FIG. 4, the flow path widening region 26A is hatched for thepurpose of illustration.

Each of the bulge portions 28 has a shape bulging from a portion of asurface of the recessed portion 26 at a distance from a boundary 25between the base 24 and the recessed portion 26 (a side surface risingfrom a proximal end portion of the recessed portion 26). Each of thebulge portions 28 is formed at such a position that at least a part ofthe bulge portion 28 overlaps the flow path widening region 26A of therecessed portion 26. A side surface 28 a of each of the bulge portions28 is formed in a shape which is gradually and slightly inclined towarda center of the bulge portion 28 as a distance from the surface of therecessed portion 26 increases.

The held portion 30 is a part to be held by the second mold 200 in thesecond step. The held portion 30 is connected to the proximal endportion of the handle main body 22. With regard to the presentembodiment, a single hole 30 h is formed in the held portion 30. Thehole 30 h is used by the second mold 200 to hold the held portion 30.Therefore, as compared with a case in which a plurality of holes areformed in the held portion 30, strength of the second mold 200 issecured.

The shaft portion 40 is connected to the distal end portion (upper endportion in FIG. 4) of the handle portion 20, and has such a shape whichallows the shaft portion 40 to be inserted into interdental spaces. Theshaft portion 40 has a shape extending straight. The shaft portion 40has a sectional area (an area of a section along a plane orthogonal tothe axial direction of the shaft portion 40) smaller than a sectionalarea of the handle portion 20. The shaft portion 40 has a substantiallycircular columnar shape. More specifically, the shaft portion 40 isformed into the shape having an outer diameter gradually and slightlyreducing from the proximal end portion toward the distal end portion.The shaft portion 40 is formed integrally with the handle portion 20. Anorientation (attitude) of the shaft portion 40 with respect to thehandle portion 20 is set so that an angle between a tangent to thedistal end portion of the back-side edge portion 22 b and the axialdirection of the shaft portion 40 is smaller than an angle between atangent to the distal end portion of the belly-side edge portion 22 aand the axial direction of the shaft portion 40.

It is preferable from a viewpoint of smooth flow of the elastomer thatan angle θ (c.f. FIG. 4) between a first straight line L1 extendingthrough the center of the shaft portion 40 and a second straight line L2is preferably set to 10° to 50°. The second straight line L2 is astraight line extending through a first midpoint P3 and a secondmidpoint Q3. The first midpoint P3 is a midpoint between an intersectionpoint P1 of a first circle C1 in a first radius (45 mm in the presentembodiment), which is centered at the distal end portion 40 a of theshaft portion 40, with the belly-side edge portion 22 a and anintersection point P2 of the first circle C1 with the back-side edgeportion 22 b. The second midpoint Q3 is a midpoint between anintersection point Q1 of a second circle C2 in a second radius (50 mm inthe present embodiment), which is centered at the distal end portion 40a of the shaft portion 40, with the belly-side edge portion 22 a and anintersection point Q2 of the second circle C2 with the back-side edgeportion 22 b.

As shown in FIG. 3, the soft portion 50 includes a cleaning portion 60configured to clean interdental spaces, a slip resistance portion 70 anda coupling portion 80.

The cleaning portion 60 is provided around the shaft portion 40. Thecleaning portion 60 includes a cleaning portion main body 62 having sucha shape as to cover a surface of the shaft portion 40 and brush hairs64. Each of the brush hairs 64 protrudes outward in a directionorthogonal to the axial direction of the shaft portion 40 from an outerperipheral surface of the cleaning portion main body 62 and has an outershape gradually getting smaller as a distance from the outer peripheralsurface of the cleaning portion main body 62 increases. With regard tothe present embodiment, each of the brush hairs 64 is formed in a coneshape.

The slip resistance portion 70 is formed on the surface of the recessedportion 26. As shown in FIGS. 7 and 8, a surface of the slip resistanceportion 70 and the surface of the base 24 are formed to be flush witheach other. On the other hand, as shown in FIG. 8, a surface of each ofthe bulge portions 28 protrudes a predetermined dimension D (0.15 mm inthe present embodiment) from the surface of the slip resistance portion70 and the surface of the base 24.

The coupling portion 80 couples the cleaning portion 60 and the slipresistance portion 70. More specifically, the coupling portion 80couples the cleaning portion 60 and the slip resistance portion 70 on asurface of the distal end portion of the back-side edge portion 22 b ofthe handle main body 22. A sectional area of the coupling portion 80 issmaller than a sectional area of the cleaning portion main body 62 and asectional area of the slip resistance portion 70.

FIG. 5 shows a section of the cleaning portion 60 at the proximal endportion, and FIG. 6 shows a section of the coupling portion 80 at thedistal end portion. As shown in FIGS. 5 and 6, an area of the elastomerat the distal end portion of the coupling portion 80 (hereinafterreferred to as “coupling portion distal end portion area”) is smallerthan an area of the elastomer at the proximal end portion of thecleaning portion 60 (hereinafter referred to as “cleaning portionproximal end portion area”). In detail, a ratio of the coupling portiondistal end portion area to the cleaning portion proximal end portionarea is preferably between 40% and 90% (inclusive), more preferablybetween 50% and 85% (inclusive), and yet more preferably between 65% and85% (inclusive). With regard to the present embodiment, the ratio is setto 70%.

A method for manufacturing the interdental cleaner 2 is described withreference to FIGS. 9 and 10. The manufacturing method includes the firststep and the second step as described above.

In the first step, the composite material (material including thesynthetic resin, the glass fiber and titanium dioxide) is filled intothe first mold 100 having the first space in correspondence to the baseportions 10 from gates foamed at positions in correspondence to theproximal end portions of the base portions 10. In this manner, the baseportions 10 are molded. Although not illustrated, the first space is aspace having a shape in conformity to the base portions 10 connected toeach other by the connecting portions 32.

In the second step, the second mold 200 having the spaces for formingthe soft portions 50 on the base portions 10 is used. In this step, thebase portions 10 are situated in the second mold 200 at first. Indetail, the base portions 10 are situated in the second mold 200 so thatholding portions 202 of the second mold 200 are fitted in the holes 30 hin the held portions 30 and that the bulge portions 28 of the baseportions 10 are fitted with inner surfaces of the second mold 200. Atthis time, since the side surface 28 a of each of the bulge portions 28is formed in the shape which is gradually and slightly inclined towardthe center of the bulge portion 28 as the distance from the surface ofthe recessed portion 26 increases, each of the bulge portions 28 isguided so as to be fitted with the inner surface of the second mold 200,even if each of the bulge portions 28 is slightly displaced from theposition in which the bulge portion 28 is to be fitted with the innersurface of the second mold 200. Then, the elastomer is filled into thesecond mold 200 in this state. In detail, the elastomer is injected fromgates 204 formed at positions of the second mold 200 in correspondenceto the distal end portions of the shaft portions 40. In this way, theelastomer flows from peripheries of the shaft portions 40 toward therecessed portions 26.

With regard to the present embodiment, the ratio of the coupling portiondistal end portion area (the flow path area in the section at the distalend portion for the elastomer around the distal end portion of theback-side edge portion 22 b of each of the handle main bodies 22) to thecleaning portion proximal end portion area (the flow path area in thesection of the proximal end portion for the elastomer around theproximal end portion of each of the shaft portions 40) is set to 70%, sothat it is possible to suppress a very large pressure loss when theelastomer flowing along each of the shaft portions 40 flows through thespace in correspondence to each of the coupling portions 80. Therefore,the elastomer flows smoothly from the space around each of the shaftportions 40 toward the space in correspondence to each of the slipresistance portions 70 through the space in correspondence to each ofthe coupling portions 80. In this way, it is possible to suppressleakage of the elastomer from the second spaces in the second step.Since the ratio is set to 70%, a pressure loss is secured to some extentwhen the elastomer flows through the space in correspondence to each ofthe coupling portions 80. In this way, since the elastomer is filledinto the spaces in correspondence to the respective brush hairs 64,occurrence of incomplete molding of each of the cleaning portions 60 issuppressed.

Then, when the elastomer is further filled along each of the recessedportions 26, the elastomer collides with the side surface 28 a of eachof the bulge portions 28 before colliding with the boundary 25 betweenthe base 24 and the recessed portion 26 (the side surface rising fromthe proximal end portion of the recessed portion 26). At this time, aflow velocity of the elastomer reduces. Then, the elastomer collidingwith the side surface 28 a of each of the bulge portions 28 flows aroundthe bulge portion 28 and reaches the boundary 25. In this way, theelastomer is prevented from strongly colliding with the boundary 25between the recessed portion 26 and the base 24. As a result, in thesecond step, it is possible to suppress leakage of the elastomer fromthe second spaces in the second mold 200 to the outside of the secondspaces.

Through the aforementioned steps, the interdental cleaner group 1including the interdental cleaners 2 is formed. With regard to theinterdental cleaner group 1, it is possible to take an image of theinterdental cleaner group 1 to check for insufficient filling (shortshot) of the elastomer near the bulge portions 28. In detail, each ofthe bulge portions 28 is formed as a floating structure in the slipresistance portion 70 made of the elastomer, so that it is possible tocheck for the insufficient filling by checking whether the elastomer isfilled appropriately to surround each of the bulge portions 28.

With regard to the aforementioned embodiment, since each of the shaftportions 40 and each of the handle main bodies 22 are slightly displacedtoward each of the belly-side edge portions 22 a with each of theholding portions 202 as a fulcrum due to an injection pressure of theelastomer when the elastomer flows along each of the back-side edgeportions 22 b in the second step, the space for forming each of thecoupling portions 80 (the flow path area for the elastomer) is secured.As a result, the elastomer smoothly flows toward each of the recessedportions 26.

Since each of the base portions 10 is molded to have a smaller anglebetween the tangent to the distal end portion of the back-side edgeportion 22 b and the axial direction of the shaft portion 40 than anangle between the tangent to the distal end portion of the belly-sideedge portion 22 a and the axial direction of the shaft portion 40 in thefirst step, the elastomer further smoothly flows from the periphery ofeach of the shaft portions 40 toward each of the recessed portions 26 inthe second step.

Since each of the bulge portions 28 is at least partially situated ineach of the flow path widening regions 26A, it is possible tomanufacture the interdental cleaners 2 with effective slip resistancefunctions of the slip resistance portions 70 with suppressing occurrenceof jetting near each of the flow path widening regions 26A when theelastomer flows along each of the recessed portions 26 in the secondstep. In detail, if each of the flow path areas in each of the recessedportions 26 for the elastomer increases abruptly when the elastomerflows along the recessed portion 26, the jetting may occur near theposition of the abrupt increase in the flow path area. With regard tothis manufacturing method, since at least a part of each of the bulgeportions 28 is situated in each of the flow path widening regions 26A,the occurrence of the jetting resultant from the increase in the flowpath area is suppressed.

Since the composite material filled into the first mold 100 in the firststep includes the glass fiber, the base portions 10 reinforced with theglass fiber are molded. As a result, it is possible to suppress damageto the bulge portions 28 even if there is a contact between the bulgeportions 28 and the second mold 200 when the base portions 10 aresituated in the second mold 200. Vibration of the base portions 10 whenthe base portions 10 are situated in the second mold 200 may besuppressed as well.

The composite material further includes titanium dioxide. Although thereinforcing effect of the glass fiber on the base portions 10 isslightly reduced by the inclusion of titanium dioxide, the bulgeportions 28 provided to the base portions 10 suppress the reduction instrength of the handle portions 20 resultant from the inclusion oftitanium dioxide and the resultant vibration of the base portions 10 inpositioning of the base portions 10 in the second mold 200. It is alsopossible to mold the white base portions 10 at low cost. It ispreferable from a viewpoint of suppressing the reduction in strengththat material used to obtain the white base portions 10 is zinc sulfide.

Since the base 24 extends continuously along the belly-side edge portion22 a, the handle portion 20 has higher strength as compared to a case inwhich a part of the slip resistance portion 70 made of the elastomer isprovided along the belly-side edge portion 22 a, for example.

The embodiment disclosed this time is merely an example in every respectand should not be considered restrictive. The scope of the invention isnot defined in the aforementioned description of the embodiment but isdefined in claims and includes meanings equivalent to the claims and allmodifications in the scope of the claims.

For example, injecting positions of the elastomer in the second step,i.e., the positions of the gates 204 are not restricted to those in theaforementioned example. The gates 204 may be provided at positions incorrespondence to portions of the base portions 10 between the shaftportions 40 and the bulge portions 28. In this way, the elastomerflowing along each of the recessed portions 26 becomes likely to collidewith the side surface 28 a of each of the bulge portions 28, so thatoccurrence of so-called jetting is suppressed near each of the bulgeportions 28.

The recessed portion 26 and the slip resistance portion 70 may beprovided to only one surface of the handle main body 22.

As the first mold 100 and the second mold 200, it is possible to use amold including a lower mold and an upper mold for forming a first spaceand a second space with the lower mold, the lower mold including a basemold and a rotatable mold. The rotatable mold is a mold which isrotatable with respect to the base mold with holding the held portion 30of the base portion 10. The base mold has portions configured to form aspace in correspondence to the handle main body 22 and the shaft portion40, and a space in correspondence to the soft portion 50. The rotatablemold has a portion configured to form a space in correspondence to theheld portion 30. In a case of using the lower mold and the upper mold,composite material is filled into the first space formed between thelower mold and the upper mold in the first step. Then, after the firststep, the upper mold separates from the lower mold upward whereas therotatable mold separates from the base mold upward with holding the heldportion 30 and rotates 180° in the position, and is displaced toward thebase mold again. In this way, the base portion 10 is situated in thespace in correspondence to the soft portion 50 (the region below thesecond space) in the lower mold . Then, the upper mold conies intocontact with the lower mold to form the first space and the secondspace. Subsequently, in the second step, elastomer is filled into thesecond space. In synchronization with the second step, the compositematerial is filled into the first space (the first step is performed).Through the aforementioned steps, the interdental cleaners aremanufactured continuously.

REFERENCE SIGNS

-   1 group of interdental cleaners-   2 interdental cleaner-   10 base portion-   20 handle portion-   22 handle main body-   22 a belly-side edge portion-   22 b back-side edge portion-   24 base-   26 recessed portion-   28 bulge portion-   30 held portion-   40 shaft portion-   50 soft portion-   60 cleaning portion-   70 slip resistance portion-   80 coupling portion-   100 first mold-   200 second mold

The invention claimed is:
 1. A method for manufacturing an interdentalcleaner, the method comprising: a first step of molding a base portionby filling composite material including synthetic resin into a firstmold having a first space in correspondence to the base portion whichincludes a handle portion having a shape that is at least partiallycurved and a shaft portion connected to a distal end portion of thehandle portion, the shaft portion having a sectional area smaller than asectional area of the handle portion and a shape which allows the shaftportion to be inserted into an interdental space; and a second step offorming a cleaning portion configured to clean the inter dental space, aslip resistance portion and a coupling portion configured to couple thecleaning portion and the slip resistance portion by filling elastomerinto a second mold from a side of a distal end portion of the shaftportion under a condition in which the base portion is situated in thesecond mold, the second mold having a second space configured to formthe cleaning portion around the shaft portion, the slip resistanceportion on a surface of the handle portion, and the coupling portion ona surface of the handle portion, wherein what is used as the second moldin the second step has a ratio of a flow path area for the elastomer ina section of the second space around the distal end portion of thehandle portion to a flow path area for the elastomer in a section of thesecond space around a proximal end portion of the shaft portion, theratio being no less than 40%.
 2. The method for manufacturing aninterdental cleaner according to claim 1, wherein what is used as thesecond mold in the second step has the ratio which is no more than 90%.3. The method for manufacturing an interdental cleaner according toclaim 2, wherein in the first step, what is molded has the handleportion including a base and a recessed portion having a shape recessedfrom a surface of the base, the handle portion including a back-sideedge portion, which is formed on one side in a direction orthogonal toan axial direction of the shaft portion to have a curved shape so thatthe recessed portion is formed at a position including at least a partof the back-side edge portion, and a belly-side edge portion, which isformed on another side to have a curved shape so that the base is formedat a position including at least a part of the belly-side edge portion,an angle between a tangent to a distal end portion of the back-side edgeportion and the axial direction of the shaft portion being smaller thanan angle between a tangent to a distal end portion of the belly-sideedge portion and the axial direction of the shaft portion, and whereinin the second step, the elastomer is filled into the second mold so thatthe elastomer flows along the shaft portion and the recessed portion. 4.The method for manufacturing an interdental cleaner according to claim2, wherein in the first step, the composite material including thesynthetic resin and glass fiber is filled into the first mold.
 5. Themethod for manufacturing an interdental cleaner according to claim 1,wherein in the first step, the composite material including thesynthetic resin and glass fiber is filled into the first mold.
 6. Themethod for manufacturing an interdental cleaner according to claim 5,wherein in the first step, the composite material further includingtitanium dioxide is filled into the first mold.
 7. A method formanufacturing an inderdental cleaner, the method comprising: a firststep of molding a base portion by filling composite material includingsynthetic resin into a first mold having a first space in correspondenceto the base portion which includes a handle portion having a shape thatis at least partially curved and a shaft portion connected to a distalend portion of the handle portion, the shaft portion having a sectionalarea smaller than a sectional area of the handle portion and a shapewhich allows the shaft portion to be inserted into an interdental space;and a second step of forming a cleaning portion configured to clean theinter dental space, a slip resistance portion and a coupling portionconfigured to couple the cleaning portion and the slip resistanceportion by filling elastomer into a second mold from a side of a distalend portion of the shaft portion under a condition in which the baseportion is situated in the second mold, the second mold having a secondspace configured to form the cleaning portion around the shaft portion,the slip resistance portion on a surface of the handle portion, and thecoupling portion on a surface of the handle portion, wherein what isused as the second mold in the second step has a ratio of a flow patharea for the elastomer in a section of the second space around thedistal end portion of the handle portion to a flow path area for theelastomer in a section of the second space around a proximal end portionof the shaft portion, the ratio being no less than 40%, and wherein inthe first step, what is molded has the handle portion including a baseand a recessed portion having a shape recessed from a surface of thebase, the handle portion including a back-side edge portion, which isformed on one side in a direction orthogonal to an axial direction ofthe shaft portion to have a curved shape, and a belly-side edge portion,which is formed on another side to have a curved shape so that the baseis formed at a position including at least a part of the a belly-sideedge portion, an angle between a tangent to a distal end portion of theback-side edge portion and the axial direction of the shaft portionbeing smaller than an angle between a tangent to a distal end portion ofthe belly-side edge portion and the axial direction of the shaftportion, wherein the back-side edge portion has a larger radius ofcurvature than that of the belly-side edge portion, wherein the recessedportion extends along the back-side edge portion from a distal end ofthe recessed portion to a proximal end of the recessed portion, andwherein in the second step, the elastomer is filled into the second moldso that the elastomer flows along the shaft portion and the recessedportion.
 8. The method for manufacturing an interdental cleaneraccording to claim 7, wherein in the first step, what is molded as thebase portion includes the base having a shape extending continuouslyalong the belly-side edge portion.
 9. The method for manufacturing aninterdental cleaner according to claim 8, wherein in the first step, thecomposite material including the synthetic resin and glass fiber isfilled into the first mold.
 10. The method for manufacturing aninterdental cleaner according to claim 7, wherein in the first step, thecomposite material including the synthetic resin and glass fiber isfilled into the first mold.
 11. A method for manufacturing aninderdental cleaner, the method comprising: a first step of molding abase portion by filling composite material including synthetic resininto a first mold having a first space in correspondence to the baseportion which includes a handle portion having a shape that is at leastpartially curved and a shaft portion connected to a distal end portionof the handle portion, the shaft portion having a sectional area smallerthan a sectional area of the handle portion and a shape which allows theshaft portion to be inserted into an interdental space: and a secondstep of forming a cleaning portion configured to clean the inter dentalspace, a slip resistance portion and a coupling portion configured tocouple the cleaning portion and the slip resistance portion by fillingelastomer into a second mold from a side of a distal end portion of theshaft portion under a condition in which the base portion is situated inthe second mold, the second mold having a second space configured toform the cleaning portion around the shaft portion, the slip resistanceportion on a surface of the handle portion, and the coupling portion ona surface of the handle portion, wherein what is used as the second moldin the second step has a ratio of a flow path area for the elastomer ina section of the second space around the distal end portion of thehandle portion to a flow path area for the elastomer in a section of thesecond space around a proximal end portion of the shaft portion, theratio being no less than 40%, wherein in the first step, what is moldedas the base portion includes the base having a shape extendingcontinuously along the belly-side edge portion, wherein in the firststep, what is molded has the handle portion including a base and arecessed portion having a shape recessed from a surface of the base, thehandle portion including a back-side edge portion, which is formed onone side in a direction orthogonal to an axial direction of the shaftportion to have a curved shape so that the recessed portion is formed ata position including at least a part of the back-side edge portion, anda belly-side edge portion, which is formed on another side to have acurved shape so that the base is formed at a position including at leasta part of the belly-side edge portion, an angle between a tangent to adistal end portion of the back-side edge portion and the axial directionof the shaft portion being smaller than an angle between a tangent to adistal end portion of the belly-side edge portion and the axialdirection of the shaft portion, wherein in the second step, theelastomer is filled into the second mold so that the elastomer flowsalong the shaft portion and the recessed portion, and wherein in thefirst step, what is molded as the handle portion further includes abulge portion bulging from a portion of a surface of the recessedportion at a distance from a boundary between the base and the recessedportion.
 12. The method for manufacturing an interdental cleaneraccording to claim 11, wherein in the first step, what is molded as therecessed portion includes a flow path widening region in which a flowpath area for the elastomer at a portion distant by 1 mm from a specificportion of the recessed portion to an opposite side from the shaftportion is larger by no less than 7% in comparison with a flow path areafor the elastomer at the specific portion, and the bulge portion whichis at least partially situated in the flow path widening region.
 13. Themethod for manufacturing an interdental cleaner according to claim 12,wherein in the first step, the composite material including thesynthetic resin and glass fiber is filled into the first mold.
 14. Themethod for manufacturing an interdental cleaner according to claim 7,wherein in the first step, the composite material including thesynthetic resin and glass fiber is filled into the first mold.